Airplane carburetor



Feb. 18, 1941. KITTLER 2,232,392

AIRPLANE CAHBURETOR Filed Oct. 24, 1956 4 Sheets-sheet 1 INVENTOR. Nu.TON J. M TTL 5/? ATTORNEY.

Feb. 18, 1941.

M. J. KITTLER 2,232,392

AIRPLANE CARBURETOR Filed Oct. 24, 1936 4 Sheets-Sheet 2 INVENTOR. /7/L7012/ d. Mr TLEIF" ATTORNEY.

Feb. 18, 1941.

M. J. KITTLER AIRPLANE CARBURETOR Filod' Oct. 24, 1936 4' Sheets-Sheet 43 &

INVENTOR. lf/ TT 0?.

ATTORNEY.

I711. ro/v '0. BY W Patented Feb. 18, 1941 2.232.392 AIRPLANE CARBURETORMilton J. Kittlcr, Detroit, Micln, assignor, by

mesne assignments, to Chandler-Evans Corporation, Meriden, Conn., acorporation of Delaware Application October 24, 1936, Serial No. 107,386

The object of this invention is to provide an improved carburetor foruse on airplanes. Speciflcally the carburetor is of the type in whichthe fuel is admitted ahead of the throttle and the throttle is formed bytwo rollers or valves rolling together so as to provide therebetween avariable passage, approximately of Venturi form. The difllculty withsuch a construction is that the throttle valves, if unbalanced, requiretoo The, carburetor is provided with fuel from a constant pressuresupply chamber, the pressure in which may be controlled by a spring andalso by the. vacuum in the throat of the variable venturi. when acarburetor of this type is connected to asupercharger it is desirable tohave an increased flow of fuel and the pressure generated by thesupercharger is utilized to change the pressure in the constant pressurefuel supply chamber. Means for doing this so that the fuel supply can bevaried, is provided. An important advantage of the construction shown isthat the mixture ratio is approximately constant through a wide range ofmuch effort to operate.

variations in altitude.

Figure 1 shows a cross sectional elevation of a carburetor with thethrottle closed.

Figure 2 shows a cross sectional elevation with the throat open and withthe mixture controlled for use in conjunction with a supercharger shownin outline only and shows a modification of the carburetor shown inFigure 1.

Figure 3 shows the effect on the mixture of varying the pressure in thefuel supply chamber.

Figure 4 shows diagrammatically the arrangement of the carburetor,supercharger and fuel pump and the connections.

Fig. 5 shows the mixture controlled valve in the rich position.

Figure 6 is a cross sectional plan view taken on plane 5- 8 of Figure'7.

Figure '7 is a cross sectional elevation takenon plane 'I--l of Figure6.

Figure 8 shows a plan view taken on plane 8-8 of Figure 1.

'Figure 9 is a view in perspective of one of the carburetor throttles.

5 Claims.

phragms K and J with the needle valves C, C so that as the diaphragmsexpand or move relatively from one another and increase the volume ofthe chamber T, the valves C, C are moved to closed position. The effectof the spring B in 5 drawing the diaphragms K, J together is increasedby the weight Rsupported by the spring B. These flexible diaphragms Kand J segregate the air chamber L and the air chamber M from the chamberT, and the two chambersL and M 10 are in communication with each otherthrough the passage D. This passage D communicates through a passage Fwith a passage G hich communicates through nozzle openings t. with themain air passage, the openings Q being 10- cated in the most restrictedportion of the variable venturi formed between the two throttles 3| and30 which are geared together, for simultaneously opening and closingmovements, by means of the gears and I9.

A valve F controlled by the lever 21 regulates the connection betweenopening Q and the chambers L and M. In the main air entrance S to thecarburetor a pipe N extends facing against the stream of air flowing tothe engine. In Fig- 25 ure 1 the passage N communicates with the passageF through the restriction N so that the pressure, or more correctly thedepression, in the chambers L and M is determined by the restriction Nand by the extent of opening of the valve F.

The fuel flows from the chamber T through a restriction P located abovethe level of the chamber T. A needle valve Ill controls the fuel flowthrough this restriction P. This valve is operated by means of a leverl3 which engages with the shoulder i2 at one end and is fulcrumed by thepivot 28 at the other. A throttle control rod l6, when rotated, movesthe lever i3 to the right and back again by means of the roller M whichengages 'with a box cam l5 bolted to the shaft W. The gear I1 mounted onthe shaft l6 engages with another gear I! mounted concentrically withthe gear l9 and bolted to the throttle 30 so that as the shaft I6 isrotated in an anti-clockwise direction, the valve Ill moves to the rightand the throttle valves 30, 31 open up to permit more air to flow pastthe valve outlets Q, Q. An air entrance H permits air to flow around theneedle valve l0 and through flutes 25. These flutes are located in theneedle valve Ill opposite the guide 26 so that the flutes constitute aby-pass around this guide, thus permitting air to flow from II to thefuel outlets Q and to thus reduce the fuel flow past P. This outlet H,as shown, is a fixed orifice. A passage 2|, 22 is controlled by needlevalve 23 and admits additional air over and above that passed throughthe fixed opening The air flowing through the passage 2|, 22 flows intothe annulus around the needle valve l0 through the passage 24. Themovement of the needle valve I0 regulates the air bleed, that is to say,the quantity of air admitted through the passage H and also admittedthrough the passages 2| and 22. When the throttle is closed and theengine is idling a considerable volume of air is admitted through theflutes 25 in the needle valve In, which air dilutes the fuel flowingdown G and thus reduces the suction on the orifice P.

As the throttle opens, the flutes 25 cease to function as passages forair. The needle valve moves to the right and the admission of airthrough the openings 22 and II is no longer effective because themovement of the flutes to the right cuts off a path for the air. Thuswhen the throttle is more than half open, no air at all is admittedthrough the passages H and 22. The throttles 30, 3| engage with theflexible seals 6|, 62 through a circular are shown in Figs. 1 and 2 andthe lower portions of the throttles 30, 3| fit closely at their endsagainst the main body of the casting. The hollow space between thethrottles 30, 3| and the main body of the casting is maintained at thepressure in the throat of the venturi by means of the openings 59 and 60so that the effort required to operate the throttle mechanism is thusgreatly diminished. The presence of these openings 59, 60 renders theconstruction practical, as without them the effort necessary to rotatethe throttle might make the device difficult to use, commercially.

The depression back of the throttle is naturally greater than in themixture outlet 0. A passage 64 communicates this depression to thechamber 58. This chamber is separated from a chamber 54 by the flexiblediaphragm 55. The reduced pressure thus created in 58 causes thediaphragm 55 to move to the right, compressing the springs 52. Theopening 5| serves to modify the effect of the depression due to theopening 59 but as 5| is much smaller than 64, the major factor indetermining the pressure in 58 is the opening 59, Fuel is admitted tothe chamber 54 through an opening from chamber T controlled by the checkvalve 53 which is spring loaded. A fuel passage 56 serves as an outletfrom the chamber 54 and the spring loaded valve 51 serves as a fueloutlet into the air entrance. This whole structure just referred toconstitutes the automatic accelerating fuel pump which functions whenthe throttle is opened wide momentarily to increase the fuel supply andis fully described and claimed in my co-pending application Serial No.107,961, filed October 26, 1939.

In Figure 2, 50 is the supercharger which is adapted to be connected tothe mixture outlet 0. A pipe V communicates the pressure created by thesupercharger 50 with a closed chamber 33 in which is supported aflexible bellows 34 which is reinforced by a spring 35 and carries withit a valve 36. The compressed air in V thus may be admitted through arestriction 31 to a restriction 39 which leads to pipe X whichcommunicates with the chamber L. A cross passage 40 communicates withthe mixture control valve to be described later. A pipe W connects thepipe N in the air entrance S through a restriction 38 with the pipe X. Apipe Y connects the passage F with the mixture control valve. As statedabove, the passage F communicates through the valve F with the Venturithroat Q. Considering now the valve shown in Figures 2; 5, 6 and 7, thepressure communicated through passage X is modified by the vacuumcommunicating through the passage Y, depending upon the position of thevalve shown in Fig. 7.

This valve is. shown in cross sectional plan and elevation in Figures 6and 7, and diagrammatically in Figures 2 and 5. In Figures 5, 5 and 7,41 ('Fig. 6 only) is the valve lever carrying a key 46 which causes adisc valve 45- to rotate. This valve is mounted in a casting 48 which isbolted to another casting 49, whose face is the valve seat. In the valveseat there is a groove 44 which communicates through a slot 43 with anannular groove 42 in the disc valve 45. Another groove 4| in the lowerhalf 49 communicates with the pipe X. The groove 44 communicates withthe pipe Y. There is thus a connection from the passage Y to the passageX through the narrow slot 43.

In the position shown in Fig. 5, this comm-unication is cut off and inthe position shown in Fig. 2 this communication is wide open. In theposition shown in Fig. 2 there is thus a relatively free communicationfrom the low pressure in Y through the narrow groove 43 through the slot42 through the groove 4| through the passage 40 to the pipe X.Obviously, at any intermediate position the pressure in the chamber Lcan be regulated, It is also obvious that as the pressure created by thesupercharger increases, the pressure in the chamber M increases. Thepipe W connects the air pressure in the air entrance S through theopening N. This pipe W communicates with the chambers L and M and thusmodifies the pressure therein. The relative effect of the pressure inthe air entrance S is determined by the restriction 38. The smaller thisrestriction relative to the restriction 31 the less effective is thepressure in the air entrance S in modifying the effect of the pressurecreated by the supercharger 50 which is transmitted through the passageV, and through the restriction 31 and so through the restriction 39 andthe passage X to the chambers L and M.

Operation Discussing the construction shown in Figures 1 and 2, when thethrottles are slightly open, that is to say, more open than they areshown in Figure 1 in which figure they are shown practically closed, alarge suction occurs at the orifice Q. On the other hand, a relativelylarge bleeding action takes place through the opening so that thechannel suction in G is relatively low. As the throttles are opened, theeffect of the vent II, as well as of the air that enters through the lowspeed passage 22, is restricted because the slot portion 25 of theneedle is moved to the right and the bushing 26 restricts the airflowing through the slot 25 into the channel G. Therefore, thedepression in G reaches a maximum, When the throttle reaches theposition shown in Figure 2, the pressure in G rises again. The positionshown in Figure 2, however, is only reached when the airplane issuificiently high so that the admission of air freely to the carburetorwill not cause undue pressure in the cylinder head. Therefore, duringthe period of time the plane is climbing to the normal flying altitudes,the throttles are gradually opening and the depression in the channel Gis gradually diminish- 111g. The effect of this is that the normaltendency for the mixture to get richat altitude is neutralized by thediminished suction on the fuel orifice P. When the plane reaches thenormal flying elevation, the throttles are substantially wideopen.

Discussing nextFigure 2 and the means whereby the diaphragm chamber T issubjected to the suction in the passage G, there are the followingconnections.

The passage G communicates with the passage F through the opening F,controlled by a valve which in its turn is controlled by the lever 21.

The passage F communicates through the passage Y with the channel shownin Figure 6. This channel is formed in the seat of a valve con trolledby the handle 41 (see Figure 6), This valve contains an annular passage'42 and the annular passage 42 is provided with a slot 03 which may bebrought into the register with the annular channel 44 in the seat of thevalve. Obviously the valve may be rotated so that the annular slot 43 ispartially or wholly in communication with the annular channel 44. Thevalve may then be rotated so that the annular slot is disconnected fromthe annular channel II, in which case the effect of channel suction in Gceases to have any bearing on the suction or pressure in the diaphragmchamber T.

In the position shown'in Figure 2, however, the suction in G has itsmaximum efi'ect on the diaphragm chamber T because after flowing throughthe annular slot 43 the suction enters the annular passage 42 which iscontrolled by the valve lever 01. This communicates with another annularpassage 4i also located in the valve seat. This, in its turn,communicates with the passage 40 which communicates through the passageX with the air chambers L and M which are located one on each side ofthe two diaphragms J and K which, constitute the boundaries of thediaphragm chamber '1. These two air chambers L and M are connectedthrough the passage D.

.The pipe '40 is connected through the restriction 39 and through therestriction 38 to the pipe W, which communicates with the tube N whichpro- 81 and has its influence through the restriction 8| in the passagex on the pressure existing in the .air chambers L and M located oneither side otthe diaphragms J and K which form the right hand and leithand boundaries of the diaphragm chambers T.

Discussing Figure 3, the ei'fective level in the diaphragm chamber T istreated as though T were a float chamber, and the location of theorifice P is referred to as the zero level. This level is then varied intwentieths of an inch of mercury and the pressure drop in the throat ofthe venturl, when wide open at sea level, is adjusted to be exactly oneinch of mercury. Now with one inch of mercury drop in the throat of theventuri and with a zero head on the orifice P, assumlng that there is nosyphon-ing actionand with the construction shown there is no suchsyphoning action for three reasons-(1) because of the air leakage pastthe-needle I0, (2) because of the vapor released from the fuel, and (3)because of the great diflerence in area between .the the] restrictionand the passage (3- then the mixture ratio follows thewell known law,that is, as the plane ascends in the air, the density falls and the flowof fuel caused by the air flow also falls. When the density reachesone-halt that of the air at sea level, that is at about 25,000 feetaltitude, then the flow of fuel corresponds to the square root ofone-half, namely .7 of the fuel flow at sea level. The weight 01' airtaken in, however. is "one-half, If we divide .7 by we get 1.4 as themixture ratio, namely, a mixture ratio 40% richer than the sea levelmixture ratio. This, of course, is the very well known square root lawupon which all airplane carburetor development work has been done duringthe past 22 years when airplanes first reached 25,000 feet and when wefirst had to deal with air densities of half those which prevail at sealevel, and when first this problem of rich mixture at altitude becameimportant. During these 22 years that have elapsed it has been customarytoprovide means for reducing the mixture strength at altitude on thetheory that the jects into the air entrance S. mixture strength at thisaltitude of 25,000 feet Chart Relative Ch Fuel+air Lean Air FuelEfiectlve from Locatlon density pressure head Fuel gz g ideal ,3,5

flow 7 flow mixmm Percent Percent On ound 1. 0 15 .922 1. 00 02. 2 +7. 8Lean. 2000 .95 15 .s .895 .95 94. 2 +5. 8 Do. 4000 4 15 75 865 90 96. 2+3. 8 Do. 6000- .85 15 .70 .837 .35 98.6 +1.4 D0. 8000' .8 15 65 805 8010000. 75 15 .60 774 75 103 -3 Rich. 12000. .7 -.l5 .55 .74 .7 105.2 5.2Do. 14000 65 15 .50 707 65 108.9 -8. 9 D0. 20000 .52 15 37 .607 62 117--17 D0. 25000 44 15 29 539 44 122 -22 D0. 30000 .36 15 .21 .46 .36 127--27 Do. 4000i? 25 15 .10 317 25 127 -27 Do.

It is quite obvious that the pressure in L and M must be intermediatethe pressure in the air entrance S and the suction in the channel G.

When the supercharger 50 becomes effective, the mixture ratio isenriched by the efiect of the pressure created by the supercharger 50.This pressure becomes eifective through the pipe V which communicateswith the chamber 33, which contains the exhausted bellows 34, which issupported internally by a spring 35. This bellows carries a valve 36 andtherefore the air from the supercharger is admitted through therestriction will become 40% richer unless means are provided to keep themixture within normal limits. The well known expedients are to reducethe area of the fuel orifice and alternatively to impose a vacuum in thefloat chamber above the level of the fuel contained therein. These aremanual controls and are made automatic by more or less complicated meanswhich introduce certain hazards into the operation of the carburetor.

In the construction shown, however, if there is a negative head, that isto say, if the relative level in the float chamber, or in my invention,

the diaphragm chamber, is substantially lower than the level of the fueloutlet from the nozzlc P, then this square root relationship, giving the40% rich mixture, will not exist and a correction will have to be madefor the amount the level in the float chamber, or in my case, thediaphragm chamber, is below the level of the fuel outlets. For the samereason, if the level should be higher than thejuel orifice, a correctionin the other direction must be made, These calculat-ions have been madeand set out in the chart and plotted in Figure 3. Therefore, Figure 3shows the effect of the correction for variations in the level in thefloat chamber or its equivalent, and it will be noticed that where thereis a level in the float chamber (diaphragm chamber) substantially belowthat of the level of the fuel outlet from the float chamber, then thecharacteristic of the curve between mixture ratio and altitude isentirely different, whereas if there is a positive head, thecharacteristic is unchanged, although the tendency to become rich ataltitude becomes more prominent. It is a simple matter of arithmetic tocalculate these different points set forth in the chart. 1

Variations of mixture ratio above 10,000 feet are far more importantthan the variations of mixture ratio below 10,000 feet. Below 10,000feet with the modern airplane it is not safe to open the throttle andpermit the engine to take in all the mixture that it may breathe in,Engines are designed to function at maximum power at some considerabledistance above sea level. Therefore, the throttle is only opened wide atsome considerable altitude.

We notice by examining Figure 3 that if we are only concerned with thevariations of mixture ratio above, say, 15,000 feet, then with thenozzle located at the fuel level we have a very rapid increase inmixture ratio, With the nozzle located say, .22 of an inch of mercurybelow the level, then there will be a very gradual increase in richness.Below that height the mixture ratio will be determined by the closingthe throttle and the restriction of the orifice P by the needle 10. Itfollows, therefore, that with the construction shown, the mixture ratiois substantially constant for all practical purposes, and elaboratemeans for mixture control are not needed.

Figure 9 shows the means whereby the passage F controlled by the needlevalve F, which in its turn is controlled by the lever 21, communicateswith the tube F" which terminates in the center of the variable venturi,the throttle 3| being formed with a recess so that the throttle mayclose against the nozzle T without interference from the tube F. Thetube F is out of plane with the needle valve In so that the needle valveIn can control the fuel orifice P. The advantage of the constructionshown in Figure 9 is that the eifect of the depression in the throat ofthe venturi is transmitted directly to the diaphragm chamber through thepassage F uninfluencedby the flow of gasoline down the nozzle G.

An added advantage of my invention is that when the load is increasedand the engine slowed down, the mixture automatically becomes leanerwith the negative head. This reduction in speed is in practicaluniversal use when an engine is cruising, the propeller being sloweddown at the moment the plane has cleared the ground and the buildingsnear the ground, The propeller is slowed down by an increase in pitch ofthe propeller which brings about an increase in torque, which bringsabout a decrease in R. P. M., which produces a decrease in air flow,which produces a. decrease in the suction on the orifice P, whichresults in a leaner; mixture for cruising.

What'I claim is:

1. In an airplane carburetor, fuel supply means for supplying fuel underpressure, a fuel supply chamber having a fuel entrance connected withsaid fuel supply means, a valve controlling the entry of fuel into saidsupply chamber, a flexible diaphragm for regulating the pressure in saidfuel supply chamber and connected with said control valve 80 as to closeagainst the pressure of fuel from said fuel supply means, a restrictedfuel outlet from said fuel. supply chamber, said outlet being disposedabove said dia-- phragm, a wall enclosing said diaphragm and forming anair chamber therewith, means providing a passage for air for mixing withthe fuel, means providing a venturi in the air passageway, a fuel nozzledischarging into said air passage and connected with said restrictedfuel outlet, means providing a passage connecting the air entrance withsaid air chamber, said carburetor having a mixture outlet, asupercharger having connection with a mixture outlet, means providing apressure chamber, said pressure chamber having a restricted outlet, avalve for closing the outlet from said pressure chamber, a pressureresponsive element within the last said chamber and having connectionwith said valve, means providing communication between the high pressureside of said supercharger and said pressure chamber, and means providinga passage connecting the last said restricted outlet with said airchamber.

2. In a carburetion apparatus, means providing an air intake passage toan engine, means providing a pressure source of fuel, means including aflexible'diaphragm providing a fuel chamber, said chamber being at oneside of said diaphragm and having a fuel inlet and a fuel outlet, avalve for controlling said fuel inlet, means associating said diaphragmand valve whereby movements of said diaphragm will control the inlet offuel into said fuel chamber, means for subjecting the other side of saiddiaphragm to the pressure in the air intake passage to produce a forcenormally reacting against said diaphragm tending to open said valve andto maintain a positive pressure in said fuel chamber, a superchargerhaving its intake side connected with the intake passage leading to theengine and a connection from its discharge side to the said other sideof said diaphragm for producing an additional force acting on saiddiaphragm in the same direction as the first said force producing meansupon the attainment of a predetermined pressure in the superchargerdischarge thereby to increase the positive pressure in the fuel chamberand to increase the fuel flow from said fuel outlet, a venturi in saidintake passage between said supercharger and the entrance to saidpassage, and means for modifying the force produced by said superchargerin accordance with pressure conditions at the throat of said venturi.

3. In an airplane carburetor, means providing an air supply passage,means for supplying fuel under pressure, means including a flexiblediaphragm defining a fuel supply chamber having a fuel entranceconnected with said fuel supply means, a valve controlling the entry offuel into said supply chamber and arranged to close against the pressureof fuel from said supply means, means including said flexible diaphragmaaaasoz defining an air chamber, said diaphragm being connected withsaid control valve for operation of said valve for regulating thepressure in said fuel supply chamber, means providing a venturi in saidair supply passage, a fuel nozzle discharging into said air passage atthe venturi and connected with said fuel chamber, means providing apassage connecting the entrance to said air supply passage with said airchamber, means providing a passageway connecting said air chamber withsaid air supply passage at a place adjacent to the throat of saidventuri, said carburetor having a mixture outlet, a superchargerconnected with said mixture outlet, and means providing a conduitconnecting the high pressure side of said supercharger with said airchamber.

4. In a carburetion device, an air intake passage to an engine, meansproviding a pressure source of fuel, means including a flexiblediaphragm providing a fuel chamber, said chamber having a fuel inlet anda fuel outlet comprising a restricted metering orifice, a valve forcontrolling said fuel inlet, means connecting said diaphragm and valvewhereby movements of said diaphragm will control the inlet of fuel intosaid chamber, means including an air chamber at the side of saiddiaphragm opposite to said fuel chamber and a connection between saidair chamber and the air intake passage for producing a force normallyreacting against said diaphragm tending to open said valve and tomaintain a positive pressure in said fuel chamber, the back pressure insaid fuel chamber acting on the diaphragm tending to close the valve,and a supercharger having its intake connected with the intake passageleading to the engine and having a connection between its discharge sideand said air chamber for producing an additional sustained force actingon said diaphragm in the same direction as said first force producingmeans to increase the positive pressure in the fuel chamber and toincrease the fuel flow from said fuel outlet, said additional sustainedforce increasing as the air fiow through said intake passage increases.

5. In a carburetion device, an air intake passage to an engine, meansproviding a pressure source of fuel, means including a flexiblediaphragm providing a fuel chamber, said chamber having a fuel inlet anda fuel outlet comprising a restricted metering orifice, a valve forcontrolling said fuel inlet, means connecting said diaphragm and valvewhereby movements of said diaphragm will control the inlet of fuel intosaid chamber, means including an air chamber at the side of saiddiaphragm opposite to said fuel chamber and a connection between saidair chamber and the air intake passage for producing a force normallyreacting against said diaphragm tending to open said valve and tomaintain a positive pressure in said fuel chamber, the back pressure insaid fuel chamber acting on the diaphragm tending to close the valve, asupercharger located in the intake passage leading to the engine, andhaving its discharge side connected with said air chamber for producingan additional sustained force acting on said diaphragm in the samedirection as said first force producing means to increase the positivepressure in the fuel chamber and to increase the fuel flow from saidoutlet, said additional sustained force increasing in proportion as theair flow through said intake passage increases, and a pressureresponsive means acted upon by said additional sustained force forcontrolling the intensity ofsaid force on said first mentioneddiaphragm.

MILTON J. KITILER.

